program q1001;
var
    e, i, ans: integer;
begin
    assign(input, '');
    assign(output, '');
    reset(input);
    rewrite(output);

    while not eof do
    begin
        readln(e);
        ans := 0;
        for i:=1 to e do
            ans := ans + i;
        writeln(ans);
        writeln;
    end;

    close(input);
    close(output);
end.
